A polybutylene terephthalate (PBT)-series resin is excellent in various properties such as heat resistance, chemical resistance, electric properties, mechanical properties and shaping processability (or moldability), and is used for a number of applications. Specific examples of the applications include a variety of automotive electrical components or parts (e.g., various control units, various sensors, and ignition coils), connectors, switch parts, relay parts, and coil parts. For producing these components, a plurality of shaped components or parts are bonded (or joined) to each other with the use of a bonding (or joining) means such as an adhesive, a screw cramp, a snap fit, a hot plate welding, and an ultrasonic welding. Regarding these bonding means, however, some problems have been pointed out. For example, in the case of using an adhesive, the waste of time up to curing of the adhesive, or the burden on the environment becomes an issue. Moreover, in a means using a screw cramp, the labor or the cost required for fastening increases, and in a hot plate welding or an ultrasonic welding, there is fear that a product receives a damage due to heat, vibration, and others.
On the other hand, a bonding (or joining) method by a laser welding has no damage of a product due to heat or vibration involved in the welding, and the welding process is also very simple. Thus, recently the laser welding method has been widely utilized, and has come to attract attention as a welding manner for various resin components or parts.
However, it is pointed out that, in the case of bonding a PBT-series resin with a laser welding, the resin cannot be substantially welded because of carbonization or others due to a low transmittance of a laser beam. Japanese Patent Application Laid-Open No. 26656/2001 (JP-2001-26656A) discloses that a shaped article formed from a polyester-series copolymer having a melting point within a specific range is bonded to other shaped article by welding processing to form a united shaped article. This document describes that a homopolyalkylene arylate resin (a polybutylene terephthalate, a polyethylene terephthalate, and a polyethylene naphthalate) has a low laser welding strength.
Japanese Patent Application Laid-Open No. 245481/1998 (JP-10-245481A) discloses a thermoplastic resin composition which comprises a composition composed of a thermoplastic polycarbonate resin and a thermoplastic polyester resin (such as a polyethylene terephthalate) and a methacrylic ester-series resin (graft resin) blended therewith in a proportion of 1 to 10% by weight, in which the methacrylic ester-series resin is obtained by graft-polymerizing a monomer containing a methacrylic ester as a main component in the presence of a crosslinked acrylic ester-series elastic body. This document mentions an embodiment in which a bisphenol A-based polycarbonate resin and a polyethylene terephthalate resin are used in a proportion of 1.5/1 to 4/1 (weight ratio) in the resin composition. Further, as a heat-welding method of the resin composition, a hot plate welding, a vibration welding or an ultrasonic welding is also described. In this composition, however, it is necessary to use the graft resin in order to improve welding strength of the composition, and the use of the graft resin tends to deteriorate mechanical strength, heat resistance or others of the composition.
It is therefore an object of the present invention to provide a laser weldable PBT-series resin composition having an excellent laser weldability and a high welding strength even in the case of using a PBT-series resin as a base, and a shaped article formed from the same.
It is another object of the present invention to provide a shaped article of a PBT-series resin, which is high in light transmittance and welding strength.